DE3038397A1 - DISK PLAYER SYSTEM FOR CORRECTING THE SCAN POSITION WITH INFORMATION PREVIOUSLY TAKEN FROM THE DISK - Google Patents

Description

RCA 74,462

RCA Corporation, New York, N.Y. (V.St.A.)

Optical disc player system for correlating the stylus position with information previously removed from the disc.

The invention relates to an optical disc player for Correlation of data corresponding to a current field number with data read from the optical disc with respect to a earlier field number.

To implement certain new properties in a video record player it is desirable to record certain digital information along with the video signal. Regarding this refer to the concurrent patent applications "Track Error Correction, As For Video Disc Player" by J. Rustman and M. Mindel (Vertr.Az: RCA 73317) and "Improved Digital On Video Recording And Playback System "by C. Dieterich and T. Christopher (Vertr.Az: RCA 74436) referring to the same applicant as the present application has been assigned.

In particular, it is desirable to record digital numbers such as field numbers of the video signal to be recorded represent. These numbers are recorded so that

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they correspond to the spatial locations on the plate in a known order. That in the first mentioned patent application The tracking error correction system described uses the pre-recorded digital information to keep the customer on the correct Keep track. It has been found desirable in tracking error correction systems to prevent disturbed signals cause unnecessary movement of the pickup in the player. The present invention facilitates such improvements in the insensitivity of the system to interference by providing means for identifying uncorrelated field number data, which would otherwise be considered valid data.

In the device according to the invention described here, after the first valid field number has been read by the microprocessor The next expected or predicted field number is made available to the controlled video disc player. The predicted Field number is increased periodically. When the customer, such as a tracer pen, jumps to a new information track location and there is no new field number, the microprocessor holds fixes the time and increases the predicted field number accordingly.

When the taker finds an error in the disk record and skips a number of turns, then its range of motion is limited along the radius of the image plate. For example is used in systems that use a stylus in a powered carriage due to space limitations the movement of the pen and, due to the limited response speed of the car servo system, the maximum possible spatial jump of the stylus, taking into account the most unfavorable conditions, of the order of 63 turns of the spiral Information trail lies, as was determined. According to one aspect of the present invention, when reading a new field number this with the expected field number compared. If the new field number indicates a jump of more than 63 turns, i.e. if the difference between the current field number and the expected field

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number is greater than 504 (63 times e.g. 8 fields per revolution) then it becomes the current stylus position are considered invalid because such a large increase would normally not be possible. This form of Data verification is known as range verification.

The optical disc contains a fixed number of video fields in each turn of the spiral signal track (e.g. 8 fields). The vertical sync pulses are therefore in radial alignment and divide the plate into eight pie-shaped pieces Sectors. Since the mutual spatial position of the sectors is fixed when the disk rotates under the stylus, then the sectors follow a periodically repeating sequence even if the stylus skips a series of turns.

Each field number therefore contains sector information. For example, suppose that the field numbers correspond to a Binary codes are numbered consecutively, then the last three bits correspond to each field number - in the example mentioned for eight sectors of their sector location. When a new field number is read then its last three bits will match the last compared three bits of the expected field number. If the new and expected sectors do not match, then the data concerning the current stylus position is considered invalid. The use of the field numbers for the sector check, according to one aspect of the invention, enables the sector check to be carried out using equipment parts, which are already available for the tracking error correction, and allows the sector check to be carried out without the Digital information recorded on the video signal would have to be augmented.

The field numbers represent the actual stylus position on the optical disc during playback. Each of the area and sector tests described above, which the current Correlate field number with the previous field number, correct

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also relate the current stylus position to the previous one Stylus position due to the known geometry of the optical disc.

According to one aspect of the invention, a counter is provided in a video disk player, which counts the number of past video fields between a previously determined video field number and a successively determined video field number have passed, and the field number found in the sequence becomes the field number previously determined compared, and it is determined from this whether the previously determined field number plus the number of past Correlate fields with the same sector of the optical disc as the field number found in the sequence or not.

According to a further aspect of the invention, a memory is provided in which successively determined field numbers get saved. In addition, a counter is used that counts a prescribed number of transient video fields after the storage one of the determined field numbers counts. The counter contains a predetermined field number generating generator, where this field number is equal to the previously stored field number plus the prescribed number of past video fields. Then a comparison circuit used to compare a sequential field number with the predicted field number, to determine if the detected field number is the same Has remainder after going through a fixed number (which is equal to the number of times recorded on the optical disc per spiral turn Video fields) has been divided like the remainder of the predicted field number after dividing it by the fixed number.

According to another aspect of the invention is in a video disc player means are provided that the number of past video fields between a previously determined

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Video field number and one found in the sequence Field number is determined and the field number determined in the sequence with the previously determined Field number compares to determine if the previously determined Field number plus the number of past video fields within a predetermined acceptable range of in Sequence of identified field numbers is or not.

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In the accompanying drawings show:

Figure 1 is a graphical representation of a television signal showing the vertical blanking interval between odd and even fields;

Fig. 2 is a graphical representation of the digital data scheme as it is in the disclosed recording method is used; Fig. 3 is a block diagram of an optical disk encoder; Fig. 4 is a block diagram of a video disc player;

Fig. 5 is a block diagram showing the digital data generator of the optical disc encoder 3 shows in more detail;

Figure 6 is a block diagram showing more details of the information buffer for the video disk player of Figure 4;

Fig. 7 is a circuit diagram of a device for generating an error test code of the information bits for the optical disk encoder of Fig. 5;

8 shows a circuit diagram of the information buffer, partially in block form for the video disk player according to FIG. 4;

FIG. 9 shows an embodiment of a reception control counter for the in FIG. 8 information buffer shown;

Figure 10 is a state transition diagram for the microprocessor control circuit according to Fig. 4 and

11 is a flow chart for illustrating a program algorithm for the microprocessor control circuit according to FIG. 4.

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Signal scheme

Fig. 1 shows particular details of an NTSC television signal in the scheme according to the concealed ink carrier technology as described in US Pat. No. 3,872,498 to D. Pritchard entitled "Color information translating systems" is. The interlaced odd and even fields are separated from each other by a vertical blanking interval. The television specialist easily recognizes the usual vertical blanking interval, which is a first Blanking pulse interval, a vertical sync interval, and a second Equalizing pulse interval to which a number of horizontal line intervals at the beginning of each new field. As Fig. 1 shows, the video signal information begins in line 22 * of field 1 and in the Line 284 'of field 2.

The digital information corresponding to the field number appears in the Line 17 'of field 1 and in line 280' of field 2. Digital information could just as easily be in other lines of the vertical blanking interval inserted. To show details of the digital signal scheme, FIG. 2 is the time scale during the horizontal line contained in the data (Line 17 'or line 280') stretched.

Data is presented as luminance levels: 100 mean IRE units a logical ONE and 0 IRE units (blanking level) a logical ZERO. The first data bit follows the usual horizontal sync pulse 140 and the Color sync signal 142. The frequency of the color sync signal 142 is about 1.53 MHz, i.e. the frequency of the hidden color carrier. Each data bit is transmitted synchronously with the concealed color carrier signal of 1.53 MHz. As shown in Fig. 2, each digital message includes a 13-bit start code, the denoted by B (x), a 13-bit redundancy error checking code, denoted by C (x) and 51 bits of information labeled I (x). The beginning of the next horizontal line is marked by the next Horizontal line sync pulse 140a and the color sync signal 142a. Consequently the individual data bits are synchronous with the color carrier and the entire

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digital message is synchronous with the vertical sync pulse. The data frequency can be a multiple or an (integer) fraction of an appropriate one Be color subcarrier frequency. Of course, other luminance values can also be assigned to the logic values ONE and ZERO, or a given one Luminance level can be denoted by more than one bit.

In the system described here, the data system is synchronized a start code is used with the digital message, thus avoiding the need to determine the edge of the horizontal or vertical sync pulse to have to. Synchronization error in a serial digital data system lead to (full) image errors, i.e. where the received data is reversed one or more bits are shifted out of position. Heretofore known systems for recording digital data in an encoded format for optical disks Form have shown that the edges of the sync pulses are not reliable as a time reference and lead to errors in the frame. Start codes have themselves proven to be more reliable.

The specially selected start code 1111100110101 is one of the and sonar technology known Barker codes, such as those in the Book "Group Synchronization of Binary Digital Systems" by R. H. Barker, 1953 at Academic Press, New York. Barker codes are like that chosen that the autocorrelation function of a containing a Barker code and with respect to the self-shifted signal is maximal in the case of coincidence, otherwise it is minimal. This means that when assigning a value from +1 or -1 to each bit in the start code and calculating the sum of the respective Bit products for each shift position of the start code with respect to itself, such an autocorrelation function has a sharp maximum im Coincidence trap results. In particular, a Barker code, when shifted by any odd number of digits from itself, gives an autocorrelation of 0. Shifting a Barker code any even number of digits from itself gives an autocorrelation of -1. However, if there is coincidence, the autocorrelation gives the value N, where N is the number of bits in the Barker code. If so in other words

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a Barker code is shifted any number of places from itself, then it differs by a maximum number of bit positions. In the presence of noise, this property reduces the likelihood of an incorrect start code determination in comparison to an arbitrarily chosen start code.

The information bits I (x) contain a half picture number, a volume number and a space for information bits for later expansion. The field numbers identify each field of the video signal by an individual one 18-bit binary number. At the beginning of the optical disc is the first field of the video program the field "zero". Thereafter, each field becomes consecutive numbered in ascending order. The tape numbers refer to what is recorded Video signal in a group of adjacent turns of the spiral groove, which form a ribbon-like shape. All of the material in such a grooved band is identified by a common band number. as As an example of the reel number application, after the end of the video program material is recorded, the video signal is the reel number has "sixty-three". The disk player senses tape sixty-three as the end of the program and responds by lifting the pickup off the plate.

The error check code C (x) is calculated from I (x) in the optical disk recorder. For this purpose, I (x) is multiplied by a constant H (x). The product obtained is divided by another constant g (x), and after this division the remainder (the quotient is not used) is added to a third constant M (x) and one obtains C (x).

The recorded information is checked for errors in the optical disc player, in which all the information including the start code can be entered through the mentioned constant g (x) divided. If the rest is equal to the start code B (x) then the information is considered to be free of errors. The constants H (x) and M (x) are chosen so that the rest of the information is the start code. The constant g (x) common to both the optical disk recording apparatus as is also used with the video record player, is called that Generator polynomial of the code. A specific value g (x)

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chosen, which leads to a code with the help of which errors can be determined which is particularly advantageous when used with an optical disk medium. In the system described here, those listed above are used Addition, multiplication and division processes according to special Rules are implemented that are tailored to the devices with which they are to be executed. The error coding is given in greater detail will be explained later in connection with the devices for coding and decoding.

A block diagram of a video disk encoder is shown in FIG. An image signal mixture from a source 30 is fed in an adder circuit 36 with a digital data generator 38 supplied via a line 37, Bitstream representing digital data combined linearly. A synchronizing circuit 32 provides a color subcarrier and synchronizing pulses so that the data bits generated by the digital data generator 38 are in synchronism with the am Terminal 31a are present color carriers and the digital information is encoded in the correct horizontal line of the vertical blanking interval. on the data line 39 and the field number as well as the tape number Representative information data are supplied by a device 34. The use of the information about the field number and the volume number is explained in connection with the microprocessor program (FIGS. 10 and 11) will. The digital data and the video signal are combined with each other in the adding circuit 36. Another signal processing circuit 40 prepares the composite video signal for the recording medium: this composite picture signal is of the covert type Color subcarrier and is recorded using frequency modulation techniques.

In the optical disc player of FIG. 4, the frequency modulation signal is with the aid of a pickup transducer and a stylus containing scanning device 20 scanned and processing by means of a video signal device 18 converted into a standard television signal for playback with a conventional television receiver. The video signal processing circuit 18 includes circuitry under control of the burst signal

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a 1.53 MHz oscillator is phase-synchronized with the color subcarrier. The color oscillator is in addition to its usual use for demodulating the hidden color carrier oscillation to deliver a digital one Clock signal, which appears on line 72, is used. The video signal processing circuit 18 also contains devices for demodulating the video carrier and comb filtering the demodulated video signal. A comb filter 19 subtracts two consecutive field lines, and the subtraction result appears on line 70 as a processed video signal. Since the line 16 ', in which the black level prevails, from the line 17' that is modulated with digital data are the processed ones Video signals on line 70 represent the recovered digital data. Of course, line 16 'can contain any constant luminance level. if the line 18 'following the data line 17' is a line of constant luminance (including black), then the following output of the comb filter during line 18 'again represents recovered digital data, but inverted. By subtracting one line from an adjacent line of constant luminance, the recovered digital signal becomes on its own, and data errors due to shifts in the DC level in the video signal are eliminated. If so desired is to put data on consecutive lines instead of having data next to lines of constant luminance, then there would be facilities required which the video signal to a predetermined luminance level or obtain a DC voltage reference level so that the digital data flow can be separated from the video signal.

From Fig. 4 it can be seen that the information buffer 16 when the processed video signal on line 70 and the 1.53 MHz clock signal on line 72 digital data is extracted from the video signal. The buffer is controlled by a supplied from microprocessor 10 via line 71 digital binary control signal. A binary state of the control signal on line 71 causes information buffer 16 to receive data. With the other In binary state, the control signal on line 71 conditions the information buffer 16 for the transmission of the received data to the microprocessor 10. If the control signal on the line 71 has a high level, then the information buffer 16 opens for the scanning of incoming data on line 70 carrying the processed video signal using

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of the 1.53 MHz signal on line 72 as the clock signal. After recording a complete information or message, the status signal on line 75 provides an indication that the information is complete. To the Transmission of the information to the microprocessor memory becomes the control signal on line 71 brought low. This locks the information buffer 16 and resets the internal control circuits, and the results of the information error code test are applied to the status line 75. When the status signal indicates that the information is valid (ie if the error code check results in a validity), then the microprocessor 10 is programmed for the transmission of data in the information buffer 16 to the microprocessor 10. The microprocessor delivers an external clock signal on line 73 for data transfer from the information buffer 16. With each clock pulse, one bit of the data on line 74 is transferred out of the information buffer and into microprocessor 10 pushed in. When all the data have been transferred to the microprocessor 10, the program is ready for further digital information or message, a high level appears again on the control line 71 and the process is repeated.

The microprocessor 10 controls the blanking via the information buffer 16 of line 17 '(or line 280') from the video signal. The first digital Information is obtained by constantly searching the video signal for a start code. The information buffer 16 is then blocked. Then it will be the information buffer, controlled by the timing of the first digital message, is opened for about six lines before the next digital message Message is expected. If no valid message is found, then the information buffer 16 is expected about six lines after it Time of occurrence blocked. On the other hand, it becomes a valid digital message is found, the information buffer 16 is locked and, based on the time of occurrence of the current digital message, the new Calculated time for the next digital message to appear. In this manner, the microprocessor 10 opens a gate or data window of about twelve Line width, which is centered around the expected data.

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The time interval from the middle of one data window to the next is about the time interval of a video field. The width of the data window is chosen so that in the event of the most unfavorable temporal conditions the expected data fall into the data window. Sources of timing errors, as will be explained below, are: The limited resolving power of the Digital timer, the drift rate of the timer, program uncertainties in determining the timing of the occurrence of the current data, Time differences between odd and even interlaced fields. Adjustments for the use of other microprocessors and / or timers can be done by adjusting the width of the Data window. The microprocessor program that does the logic for searching of data and the centering of the data window is described below in connection with FIGS.

The microprocessor 10 also responds to the adjusters 14 on the control panel of the turntable (hang up, pause and sample) to operate the player mechanism 12 and control of the display panel 22 of the player in accordance with a predetermined program, as will also be discussed later. Of the Player mechanism is further provided with at least one displacement device for the stylus, which is actuated by the microprocessor 10. Such a displacement device works piezoelectrically, electromagnetically or in some other way and puts the signal pick-up in neighboring ones Grooves or signal traces on the optical disc. The use of such a shift or bypass device for exiting blocked grooves is then also used in conjunction with those shown in FIGS Flowcharts described.

Error code

As stated earlier, an optical disk recorder uses the Information bits I (x) for calculating C (x). Because of the large number of Potential combinations - I (x) and C (x) together are 64 bits long - and because of the desire to have the error detection and correction properties of one given codes without the aid of an enumeration

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Error codes treated mathematically. A general mathematical development of the ring theory and Galois fields GF (2 ^m ), which are generally applicable to error codes, can be found in the publication "Error Correcting Codes" by W. Wesley Peterson in the MIT Press, Cambridge, Mass. For the purposes of this discussion, the best way to understand the error coding in the optical disc is to use a few simple definitions.

A digital message containing ONE's and ZERO's can be viewed are represented as a representation of an algebraic polynomial which contains powers of χ. The coefficients of the respective powers of χ are the individual ones Bits of the message. For example, the 4-bit message 1011 can be represented by the polynomial P (x) of the form

P (x) = 1 · χ ³ + 0 · χ ² + 1 · χ + 1 · χ °
= χ + x + 1.

If you apply this expression to the start code 1111100110101, then results themselves

B (x) = x ^l2 ₊ x ¹¹ ₊ x ¹⁰ ₊ x ⁹ ₊ x ⁸ ₊ x ⁵ ₊ x ⁴ ₊ x ² ₊ ¹ .

The highest power of χ is called the degree of the polynomial. In the above Example, B (x) is a twelfth degree polynomial.

Polynomials can be added, subtracted, multiplied and divided according to the usual rules of algebra, except for coefficients in modulo-2 expressions can be written. An abbreviation for the remainder of a polynomial after division by another polynomial is given in brackets specified. if

P (x) _ _n / _y \. r (x)
glüT * ^{Q (x) +} gTxT

and the remainder r (x) is one degree lower than the divisor g (x) then is [P (X)] = r (x).

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In the optical disc recording apparatus, the entire on the optical disc recorded message or information expressed by a polynomial T (x). From Fig. 2 follows

T (x) = B (x) x ⁶⁴ + C (x) x ⁵¹ + I (x). (1)

The term χ shifts B (x) by 64 bits because B (x) is at the beginning of the data scheme lies. Correspondingly, the term χ shifts C (x) by 51 bits, by to represent that C (x) is recorded before I (x). According to the system described, the recording device calculates a value for C (x) so that that the entire message T (x) has a remainder equal to B (x) after going through g (x) is divided. Assuming C (x) of the form

C (x) = [Kx) -H (X)] + M (x), (2)

then H (x) and M (x) are constant polynomials chosen so that

It can be shown that equations (1), (2) and (3) after solving for the constant polynomials H (x) and M (x)

H (x) = [x ¹²⁷ ]

M (x) = [B (x) x ¹³ + B (x) x ¹²⁷ ].

Fig. 7 contains a table in which selected values for B (x) and g (x) as well as the derived values for H (x) and M (x) are listed. The higher order bits are shown on the right in Fig. 7 so that they have the same order as the flip-flop memory elements in the logical diagram of the same figure appear.

The recorded digital information is stored in the optical disc player by the electronic circuits read by the player. The data recorded on the optical disk is T (x). The data read from the turntable are R (x). If there are no errors between recording and playback, then T (x) = R (x). The received message R (x) is checked for errors, by dividing R (x) by g (x). If the remainder is B (x),

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the start code, then the information is considered to be error-free. if otherwise the remainder is not equal to B (x) then this means an error.

The properties of the code generated in the above manner depend on the choice of g (x), the so-called generator polynomial. The polynomial g (x) chosen in the individual case for the optical disk is one of the computer calculated codes that Tadao Kasami in his publication "Optimum Shortened Cyclic Codes for Burst Error Correction "in IEEE Transations on Information Theory 1963. A color sync error in a digital system represents one type of error in which adjacent Bits in a digital message are lost. Color burst errors are a likely type of optical disk transmission error. As Kasami shows in the referenced reference, a code that single color sync signal that can be corrected by 6 bits or less can be used using a generator polynomial of the following type

g (x) »X ¹ VVVV ₊ X ⁶ AV ₊ I.

It can also be shown that for this polynomial g (x) all individual color sync signal errors of 13 bits or less are detected and with a probability of 99.988% of all individual burst signal errors, longer than 13 bits can also be detected. The video disc player described here only uses the error detection feature of the selected code.

As a special example of error code generation, let us assume that where the field number is 25,000, the volume number 17 and the Number of reserve bits is 0. Because 25 000 is 000 110 000 101 000 in binary and 17 is 010 001 in binary (higher order bits are on the left), the 51 information bits are 000 000 000 000 000 000 000 000 110 000 110 10t 000 010 001. The order of transmission occurs as follows: First the reserve bits, then the field number and then the tape number, with the most significant bits coming first be transmitted. The error code for the above specific expression

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I (x) is calculated and represented as the remainder of I (x) times H (x) plus M (x) through 0111100100010. The next video field is 25 001 or in binary 000 110 000 110 101 001. For corresponding information bits 000 000 000 000 000 000 000 000 000 000 110 000 110 101 001 010 001 is the correct error code 1000101101110. The complete digital information for the field 25 001 including the start code is thus 1111100110101 1000101101 110 000 000 000 000 000 000 000 000 000 000 110 000 110 101 001 010 001, shown in the order of transmission. The start code is contained in the first 13 bits, the error code in the the next 13 bits and the 51 information bits are the last. In which The optical disc player will use the digital information given above for errors checked by dividing the information obtained by g (x). If no errors are found, the remainder is 1111100110101, which exactly is the start code.

devices

A block diagram of an arrangement for generating the function T (x) is shown in fig. Under the control of the transmission control circuit 50, 24 bits of information are transmitted via the data line 39 and 27 spare information bits via the data line 39a into a 51-bit shift register

44 stored. Then I (x), which is 51 bits, becomes another 51-bit shift register 52 shifted.

At the same time, during the 51 shift pulses, an encoder calculates

45 C (x) in the following way. The polynon division and multiplication circuit 46 calculates the remainder of the 51-bit serialization of I (x) of I (x) times H (x) divided by g (x). Then, M becomes (x) in the polynomial adding circuit 48 added in parallel. The resulting code C (x) is input to a 13-bit shift register 54 and B (x), the start code, becomes is input to another 13-bit shift register 47 via the data line 49. Since the start code is a constant digital value, this entry is made preferably via fixed connections to the parallel input lines of the shift register 47, in contrast to a program implementation.

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If the logic is positive, the corresponding parallel inputs are for Shift register 47 connected to ground potential if the start code has a ZERO, and to a positive potential if the start code has a ONE. The transfer control circuit 50 controls the serial shifting out of the entire information T (x) which is in the three shift registers 52, 54 and 57 is included, in synchronism with the color carrier on line 31a. A video sync pulse supplied on line 33 is supplied the transmission control circuit 50 with a time reference signal so that the digital information is at the correct time with respect to the video signal is transmitted.

A specific embodiment of an encoder (which is denoted by 45 in FIG. 5) is shown in FIG. Clock-controlled flip-flops with output connections Q ₀ to Q ₁₂ form a residual memory. Multiplication by H (x) and division by g (x) are carried out bit-serial at the same time. The remainder is then retained at the outputs Q _Q to Q _{12 of} the remaining memory (see Chapter 7, pages 107-114 of the already mentioned book by Peterson, where such circuits are generally dealt with). In order to see how easily the circuit according to FIG. 7 multiplies and divides polynomials, it should be mentioned that both the addition and the subtraction (the coefficients of the terms of equal powers) are carried out by an EXCLUSIVE-OR gate. I (x) is multiplied by H (x) by corresponding connections with one or more EXCLUSIVE-OR gates 80 to 91. If a coefficient H (x) but not g (x) is equal to 1 (bit positions 1 , 3 and 8), then the input I (x) is connected to an input of one of the OR gates 80, 82 and 87, respectively. I (x) is divided by g (x) by multiplying the output signal from Q ₁₂ by g (x) and subtracting the resulting product from the contents of the memories Q ₀ to Q ₁₂ . If a coefficient of g (x) but not H (x) is equal to 1 (bit positions 4, 7 and 11), then the output of Q _{12 is} connected to an input of one of the EXCLUSIVE-OR gates 83, 86 and 89 connected. If H (x) and g (x) are both equal to 1 (bit positions 0, 2, 5, 6, 10 and 12) then the output of the EXCLUSIVE-OR gate 91 becomes one of the EXCLUSIVE-OR gates 81 with an input , 84, 85, 88 and 90 respectively. After 51 clock pulses,

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one for each bit of I (x), the content of the memories Q ₀ to Q _{12 is} equal to the remainder of Ι (χ) · Η (χ) after division by g (x).

Note how M (x) adds to the contents of the remaining memory will. The coefficients are added in modulo-2 arithmetic, which is performed by the EXCLUSIVE OR function. If M (x) Has coefficients of +1 then the complementary output Q of the corresponding Used flip flops. If M (x) has coefficients 0, then the becomes non-complementary output Q used.

A block diagram of a circuit for decoding the received Information R (x) is shown in FIG. 6, which shows an embodiment of the information buffer 16 according to FIG. A control signal on the line 71 forming an input conditions the receiving decoder according to FIG. 6 either for the supply of data from the video signal or to transfer data to the microprocessor.

In the receive state, each bit is stored in two separate registers at the same time inserted. One such register 60 is intended for data and another register 62 for error checking. The error check register 62 is a polynomial division circuit. However, when new data is recorded, the divider return is blocked so that a shift register results. The operation of the divider register 62 is described in detail below in connection with FIG explained. Suffice it to say for the moment that the register 62 under the control of receive control circuit 64 are either sequential Inserts bits of R (x) or divides consecutive bits of R (x) by g (x). In both cases, the content of register 62 is available the data line 78 and becomes the start code and data validity detector 66 supplied.

The reception operation begins with the conditioning of the register 62 for a shift register operation. After B (x) is detected by detector 66

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has been, the control circuit 64 conditions the register 62 for the Operation as a polynomial division circuit. Thus, the polynomial division by g (x) begins with the presence of B (x) in the divider register 62. The receive control circuit 64 also reacts to the detection of B (x) by counting a period of time which is equal to the remaining message bits (64 clock pulses) is. After this period of time, the divider 62 contains the remainder of R (x) modulo g (x), and the result should be B (x) if the information is valid. During error checking, the data register has 60 bits of data inserted. At the end of the mentioned period, the data register 60 only stores the last 24 bits. However, since the 24 information bits at the end of the Message, the register 60 contains the assigned information bits. If the reserve information bits are to be used, additional Shift register stages are added.

The interpretation of the output state signals on line 75 depends on the State of the control signal on line 71. Conditions the status signal on the line 71 the receiver for the data recording (recording status) then the status signal on the line 75 is defined as "message received". If the control signal on line 71 conditions the receiver for the data transfer (transfer state), then the status signal on line 75 means "data valid". The control signal on line 71 also sets the receiver control circuit 64 and allows the results of the residual test to reach the status signal on line 75.

The information obtained is under the control of the microprocessor external clock pulses supplied on line 73 from the shift register 60 brought out. After the data has been pushed out, the control signal on line 71 can assume its previous state again and be conditioned the receiver decoder again to continuously search for another start code.

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Fig. 8 shows, partly as a block diagram, a logic circuit of the receiver ^{decoder from Fig. 6. The flip-flops with the output connections Qq 1} to (Lp ¹ form a residual memory. The polynomial division by g (x) is carried out by multiplying successive memory output expressions of ( L 2 through g (x) and by subtracting the product (via EXCLUSIVE-OR gates 100 to 108) from the contents of the remaining memory. A feedback line from Q ₁₂ '(via NOR gate 109) leads to an EXCLUSIVE-OR gate if g (x) has coefficients of 1, except for Since the coefficients g (x) for bit positions 0, 2, 4, 5, 6, 7, 10, 11, and 12 are one, is an EXCLUSIVE-OR gate at the data input of each corresponding flip-flop of the residual memory, as shown in the figure. A NAND gate 118 determines B (x) which is both the start code and the valid error check code count down and counts 23 clock period n and then supplies a stop signal which, with the aid of a NAND gate 111, interrupts the clock feed to all decoder flip-flops. An illustrative embodiment of receive control counter 117 is shown in FIG. 9 with seven flip-flops 130-136.

The operational flow of data reception is as follows. if the control signal on the line 71 is high, then data is passed through an AND gate 110 to the division circuit 62. The flip-flop 119 has been previously set and blocks the feedback signals in the division circuit 62 by blocking the NOR gate 109. The register 62 now works as a shift register. When B (x) is detected, the output of NAND gate 118 goes low, and the Q output of flip-flop 119 goes one clock period later to a low value. Hence the feedback for the polynomial division by the output of the AND gate 120 via the NOR gate 109 restored when B (x) is found in residual memory. After 63 clock periods, the reception control counter 117 stops, and so does the status signal on line 75 goes high, which means

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"Receive information". The shift register 60 holds the last 24 bits of I (x). For data transmission, the control signal on line 71 is brought to a low value. The inverted output signal of the NAND gate 118, which is low if the remainder is after division B (x), is switched to the status signal on line 75. External clock pulses on line 73 cause successive data shifts in memory 60 to the output data signal on line 74. The external clock pulses also empty the remaining memory by inserting zeros.

The arrangement described above describes a residual memory with the same non-zero constant begins and ends. It goes without saying, however, that other arrangements are possible when using a coset code. For example, the remaining memory after determining B (x) can be set to a first arbitrary constant. After the division, the remaining memory is then checked for a correct second constant. The first or second constant can be zero, but both constants cannot.

Consider the simplified apparatus resulting from that described here Error code scheme results. Because the start code B (x) ends as a valid remainder, the start code detector (NAND gate 118) also as a detector for a valid code. Because the division begins with the start code in the division circuit, there is no control step in which the remaining memory does not have to be made empty.

Typically, error codes are placed at the end of a message. By However, the arrangement of the error code in front of the information bits looks simplified the control circuit continues because it need not distinguish information bits from error bits with respect to the data storage register 60. In addition, as shown in Fig. 8, the reception control circuit is a simple counter 117 having a start terminal and a stop terminal, who only has to count a single time interval.

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Realization of the microprocessor

With the video signal there is digital information including reel number and Field number recorded and used by the turntable to perform a Number of measures used. How the turntable uses the reel number information to determine the end of the plate (Volume 63). The information of the field numbers in ascending order is used for the calculation and display of the program playing time on a light-emitting diode display unit 22 according to FIG. 1. If the length of the program material is known, the information via the field number for calculating the remaining program playing time draw in. For NTSC signals, the elapsed program time can be calculate in minutes from the field number divided by 3600. If desired, the remaining program time can be from the previous Calculation can be determined. This feature is useful for the viewer when looking for a desired point in the program. A particularly useful one Feature derived from the information about the field number can be, is the correction of a fixed groove, which is then in Connection with the more general case of tracking error correction will be explained.

Field numbers indicate the actual position of the scanning pin. In order to the actual scanning pen position can always be determined from the first valid field number read when the scanning pen is again in a groove occurs whether it has skipped tracks or whether the sensing mechanism has been actuated. Both the tracking error correction system and the display device for the program playing time use data about the field number and are therefore divided into the decoder part of the video disk Digita Ida system. The special version of the one described here Tracking error correction system uses data on the field number (stylus position), in order to keep the stylus at or in front of its expected position, a predetermined relative speed between the stylus and recording required. The program playing time display uses the data on the field number for a display of the playing time, which is actually Figure 3 is another representation of the stylus position.

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The microprocessor control circuit operates with several internal modes of operation. 10 shows a state change diagram to illustrate the operating mode logic executed by the microprocessor program. Everyone who Circles represent a machine operating mode: insert, start, touch down, play, pause, pause lock and end. For each operating mode is the The position of the stylus and the status of the display unit are entered in the respective circle. The arrows between the operating modes show the logical ones Combination of signals from the Adjust! given on the control panel (insert, pause, scan), which cause a change from one operating state to another. The insertion signal indicates that the playback mechanism is ready to accept an optical disc. The pause signal is generated by an associated switch on the control panel is given, and the scanning signal indicates the operation of the scanning mechanism.

After switching on the power, the system goes into the insertion state, in which an optical disc can be placed on the turntable. After hanging up the turntable goes into a start-up state for several seconds about, in which the turntable is brought to full speed of 450 revolutions per minute. At the end of this start-up state the turntable goes into touchdown mode.

In the touchdown state, the digital subsystem lowers the stylus and searches continuously after a playback point, which is considered valid in touchdown mode Start code or valid error checking remainder is defined. After finding At one playback point, the system goes into playback mode.

In playback mode, the microprocessor stores an expected or predicted field number. The predicted field number is used for each field increased or renewed. For all successive readings, the microprocessor uses the predicted field number to perform two additional checks to further improve completeness (Integrity) of the data.

The first additional exam is a sector exam. The one observed here Optical disk contains eight fields per revolution, which divides the disk in eight

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Sectors is divided. As the mutual spatial location of the sectors is fixed, the sectors follow a periodically recurring sequence when the disk rotates, even if the stylus has a number of Skips grooves. Although the digital information from one or more Fields (sectors) cannot be read when the stylus jumps into a new groove, the microprocessor remembers the time and increases the predicted field number accordingly. When the stylus sits in a new groove and picks up a new digital message, then the new field number is determined by comparing it with the predicted field number checked. If the sector is wrong, then the data is considered to be a miss scan.

The field number is represented by an 18-bit binary number. From the Field number can be the sector information as the remainder after dividing the Find field number by eight. It should be noted, however, that the three lowest-digit bits of a binary number represent a modulo-8 number. Therefore, the three least significant bits of each new field number must be equal to the least significant three bits of the predicted field number to pass the sector check.

A second check for data completeness is the area check, an examination of the maximum range of stylus movement along the Plate radius. It is to be expected that in the worst case in each Operating mode no more than 63 grooves can be skipped. The groove numbers are represented by the 15 most significant bits of each field number. The microprocessor subtracts the current groove number from the predicted one Groove number. If the difference is greater than the acceptable range of 63 grooves, the current data will be considered a misread viewed. All other readings are considered correct readings and are used to update the predicted field number. After 15 consecutive If readings are incorrect, the system goes back to touchdown operation above. The presence of a scanning signal also causes a change in the touchdown operation in certain operating modes, as FIG. 10 shows.

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The microprocessor sets when the transition from set-up to playback mode the false reading count to 13. This means that when transitioning from touchdown operation in the playback mode one of the next two fields must give a good reading, otherwise the counter reaches bad Readings the value 15 and causes a return to the touchdown mode.

If the pause button is pressed during playback, this is possible System into the pause operating state, in which the follower pin is lifted off the plate and over this in the respective radial position is held. If you let go of the pause button, the turntable goes into pause lock mode and remains there. When again Pressing the pause key leaves the pause lock mode and switches to touch-up mode. When the volume number 63 is detected then the transition from the operating state Play to the operating state End takes place.

Fig. 11 shows a flow chart of the program executed by the microprocessor. The microprocessor as a device contains an interrupt line and a programmable timing device. A commercially available microprocessor, the one that is suitable for the system described here is the Fairchild Semiconductor model F8.

The microprocessor uses the timing device to control the time window, in which the information buffer searches for data. This data window is about twelve horizontal lines wide and is centered around the expected data. If no data is found, the time control device stops the internal program synchronization up to a field time interval.

The microprocessor interrupt line is connected to the one on line 75 (Fig. 4) existing state signal coupled. The interrupt lines are only activated in touchdown operation if the system is continuously following Data searches. The program is interrupted when a digital message occurs. If the error code check results in a validity, then sets

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the interruption circuit (not shown) (interrupt service routine) an interruption character. The programmable controller is then used in playback mode to determine the estimated time of occurrence of the next Specify digital message.

The input signals coming from the switches (for inserting, scanning and Pause) are in such a state that switch bounces are not undesirable Result in reactions from the turntable. The microprocessor program contains a special logic part with the help of which the input signals from the switches are made bounce-free. The values the bounce-free switch signals are stored in memory. A separate debounce count is recorded for each switch. For the bounce test 154 the switches are scanned and a comparison is made with the stored switch value. If the sampled and the stored State match, then the bounce value for that in question Switch set to zero. The switch states are as often as possible scanned. For each field (according to the NTSC standard every 16 milliseconds) all bounce counts are necessarily increased. When the resulting bounce is equal to or greater than 2, then the stored data are brought to the new (debounced) value. Then the new switch state went out.

The first programmed step (Fig. 11) after switching on the power, is the initial setting 150 of all program parameters. The time control device is set to count out a video field. The operating mode is set to insert.

The next step 152 is a program to perform the state change logic operations, as shown in FIG. The debounce counts are normally increased at this point and checked to see if a new switch state is completely bounce-free.

After the mode selection logic 152, the program enters enters a tight loop 153 to first get the debounce counts for the

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Palpable switch settings to zero if necessary, and to check the step 154 _S secondly, whether the Zeitstauergerät is already close to the end of its count, step 155, and to review third "whether the interrupt signal is set, step 156th

If the interrupt _{signal is set 3} 156 _s, then the program transfers data 157a from the information buffer and sets 157b of the time control device to count a new field interval. The program now uses the previously stored timer content to set the timer, 157b, with a corrected value that predicts the approximate time the next digital message will occur. Even if the touchdown data is the first good sample, then the miss-sample counter is set to 13, 157c

If the interrupt signal is not set _s then the program branches to the end of time counting, 155. If the unit is not in the play state 159, then the timer (timing circuit) is set for the enumeration of another field interval ₃ 158. If the unit is in the Playback state 159 then a number of time critical tasks are to be performed, 160. The data window is opened, 160a (by setting the control signal on line 71 in Figures 1-8 to a logic ONE) for six horizontal lines forward the expected dates. The recorded data is read and checked, as already mentioned. After the data _{5 has been recorded} or if no data has been recorded, the data window is closed again. The content of the timer, which represents the actual time the digital message occurred, is used as a correction factor to reset the timer, 160b. The timer is therefore set so that the next data window is above the predetermined time of occurrence of the next digital message based on the actual time of occurrence of the current digital message.

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The expected field number is reset, 16Oc, the tape number is checked for start (tape 0) and end of playback (tape 63), and the miss-scan count is incremented for a miss-scan, 160g. For valid field data in the program viewing material, the time is calculated and displayed, 16Of. If valid field data indicates that the stylus has jumped back, then the pen displacement or nudger is actuated, 160e, and the landing operation begins. When the miss-scan count reaches 15, the landing operation is also started immediately. During the time used for critical tasks.160, the switch bounce check is continued periodically so that the switches are checked as often as possible. The program immediately returns to tight loop 153 through mode select logic operations, 152, and waits for the timer test, 155, or interrupt test ₉ 156, to indicate the occurrence of the next digital message.

The timer can be set by entering it directly via programmed commands. However, rather than using a sequence of instructions, it is best to set the timer by establishing a location in memory (a marker) that corresponds to the counted-out state of the timer. The timer then runs free. The expired timer or the end of its expiry is determined by comparing the contents of the timer with the flag set in the memory. The next desired counting state is set by adding the next desired time interval to the previous timer contents and storing the result in memory. The memory is so set whenever valid data is received or when no data _s occur within the data window by adding a new flag is set in the memory corresponding to the next count state.

The programmable one used in the microprocessor in the arrangement described here Timer is caused by the program to cycle the input clock of 1.53 MHz to be divided by a factor of 200. The counter thus counts once for every 200 cycles of the 1.53 MHz clock.

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A vertical field (with NTSC a sixtieth! Second) then takes about 128 counts of the timer. You can alternatively use a timer that counts another multiple of the 1.53 MHz clock, or one which a time source independent of the video signal is used Made wide enough to accommodate multiple sources of timing error. The uncertainty of time due to the limited resolution of the timer is equal to the least significant bit, which corresponds to two horizontal lines. Because 128 timer counts do not result in exactly one vertical field, the accumulated drift error after 16 consecutive fields is in which no valid message has been encountered, slightly less than one line. Since the color subcarrier clock of 1.53 MHz is an odd multiple of half the line frequency, a timer with a corresponding Multiples of the color carrier cycle count, have a drift rate of zero. at With the special arrangement described here, the program uncertainty in determining the time of occurrence of data is about 97 microseconds, or about 1.5 lines. Because alternating fields are interleaved are, the time from one digital message to the next takes either 262 or 263 lines depending on whether the current field is odd or even. Although the program could hold tracks of odd and even fields, it is easier to just close the data window by one to enlarge additional line. Summing up the above factors, it can be shown that a data window that spans three timer counts (about six lines) both before and after the start of the expected data, even for the most unfavorable temporal states is sufficient.

Tracking error correction

As already mentioned, the information can be about the field number lead to the detection of blocked grooves. If the new field number (after the sector and area check) is smaller than the expected field number, then the stylus has jumped back and repeats the Track scanning of one or more previously played grooves, that is

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a blocked groove has occurred. If the new field number is larger than the expected field number, then the stylus has jumped forward, i.e. in the direction of the center of the plate. In the present invention skipped grooves ignored; if the new half-frame number is larger (but still passed the sector and area examination), then the expected will be Half-formation renumbered to the new field (so that it corresponds to this as the new status). In certain other use cases, for example those where the optical disc is used to record digital information on many horizontal lines, it may be necessary to skip the lines Identify and correct grooves. For the video application considered here the blocked groove is corrected by actuating a displacement or abutment device for the stylus until the latter has returned to the expected track. The stylus is then lifted over the faulty groove.

In a more general sense, the inventive use of the half-picture number information is an accurate means of determining general tracking errors. In every optical disk system with spiral or circular Traces, including optical and grooveless systems, are always track errors due to defects or contamination. That The system described here offers the possibility of determining and correcting such tracking errors in an optical disc player. For a positive Tracking is a bi-directional push or slide device provided, which forward the customer in the program material or move backwards. Thus, if a tracking error has been detected, be it a skipped or a blocked track, then will the pickup moves in such a direction that the tracking error is corrected. If you also use the normal pickup servo for purposes of Track error correction could be used, but there is a separate trigger device or repositioning device for the consumer preferable. The normal servo is generally suitable for a stable tracking of a spiral signal track and cannot die Have the right properties for responding to sudden tracking errors.

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On the other hand, a separate nudger can be specially built to respond as quickly as is necessary to correct track errors. A particular example of a kicker for use in the system described here can be found in US patent application USSN 39.358 1979 _S which the applicant also the present of E. Sims Hauser, entitled "TRACK SKIPPER APPARATUS FOR VIDEO DISC PLAYER" of 15 May Registration is transferred.

Various control or regulation algorithms are possible. The pickup can be fed back directly to correct the tracking by inducing a stylus movement proportional to the amount of tracking error detected. The pushing device can, however, also be actuated by a series of pulses, the number of pulses being proportional to the size of the track error detected. The pickup is moved a predetermined number of tracks by pulses until the stylus has returned to the expected track. In certain applications (for example in the recovery of digital data ,, which are stored on an optical disc), it may be desirable _s return the customer to the point of its running away and make a second reading test ₉ return rather than the customer in the expected track. In each case that can be obtained by use of a kicker and a suitable control logic a successful track scan ,, even if the optical disk defects or contaminants having ,, which would otherwise lead to nichtakzeptierbaren tracking errors shows up. ₅

In a digital track correction system, security against undetected data errors is particularly important to prevent _s that disturbed signals the customer unnecessarily before or reset. The data system described here reduces the probability of an undetected reading error to negligibly small values »

In a rough approximation one can estimate the probability; that sin zu-yigss digitalss input signal from the data system as valid

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Message is viewed that is an out of order Field number, so that the nudger for the stylus is operated. The random probability of a good start code is

13th
1 to 2. The random probability of a good error code is also 1 in 2. The random probability of a good field number is calculated as follows. The field numbers contain 18 bits. Because a disk has eight sectors in the system under consideration, the least significant 3 bits of each field number designate the sector number which must match the expected sector number. The remaining 15 bits, which designate the groove number, can be in a permissible range

4 O

change (_ + 63 grooves). Therefore only i26 of 2 random passes Field numbers the sector and area tests. If you take into account all safety considerations, then the probability is one

44
unnoticed error 126 to 2.

The above estimate is based on the assumption of purely random input signals without taking into account various factors that further reduce the likelihood of an undetected error.

For example, there are color sync signal interference on an optical disc track, v / o erroneous bits are next to each other, more likely than others Disturbance types. As already mentioned, the specific error code chosen detects all individual color burst signal errors up to 13 bits and also a higher percentage of all longer color bursts. As has also already been explained, choosing a non-zero remainder reduces for the error check code (a coset code) the probability continues undetected bug. Also the specially selected start code, a Barker code, reduces the likelihood that interference will become a false one Lead start code determination.

The data system described here applied to optical disk systems results in a relatively low rate of undetected errors _a and false alarms _s the other

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if unnecessary movement of the stylus would result, are significant reduced. The data security provided by the system described improves the stability of many turntable functions, such as the display the program playing time necessary for the correct operation of the recorded Depend on digital data.

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Claims (8)

TELEPHONE 089/4 7O60 06 TELEX 522 638 TELEGRAM SOMBEZ RCA 7 4462 Sch / Vu U.S. Ser. No. 084,392 dated October 12, 1979 RCA Corporation, New York, N.Y. (V.St.A.) claims 1) Optical disc player for playing a sector divided Optical disc, on the surface of which there is a spiral-shaped information track, which contains elements that are associated with represent a recorded carrier signal modulated to a video signal, wherein the video signal contains fields of the video information and each of these fields comprises an information signal of a horizontal line containing a sequentially arranged digital field number corresponding to that of the information signal containing video field, the'video signal contains a fixed number of video fields per spiral turn in such an arrangement that each of the field numbers in Is related to a corresponding sector of the optical disc, with a pickup for sensing the recorded video signal and with a detector for the field numbers, as well as with a correlation circuit for correlating successive values the determined field numbers with a previously determined 13001 7/081 2 3036397 Field number, identified by a Memory for the successive storage of successive determined field numbers, by a counter for incrementation the stored field number of each video field in terms of providing a predicted field number and by a comparison circuit for comparing successively detected field numbers with the predicted field number to determine whether the respective sector information of the ascertained Correlate field number and the predicted field number with the same sector of the optical disk or not. 2) video disc player according to claim 1, characterized in that the counter has a predetermined number of video fields counts that have passed after one of the determined field numbers has been saved, and. that-the counter is a facility for generating a predicted field number which is equal to the previously stored field number in addition to the predicted number of past video fields, and that the comparison circuit determines whether the detected field number after division by a fixed number of video fields per spiral turn gives the same remainder as the predicted one Field number after division by the fixed number. 3) video disk player according to claim 1 or 2 for correlating successive values of detected field numbers a previously determined field number, the optical disk contains eight sectors per spiral turn and the field numbers are represented in binary form, as a result of. marked, that the comparison circuit to compare the successively determined field numbers with the expected Field number means a device for providing a display signal contains if the least significant three Bits of the field number detected are equal to the least significant three bits of the predicted field number. 13001 7/081 2 -3- 1038397 4) video disc player according to claim 1, characterized in that the counter has a counting circuit for counting the predetermined Contains number of video fields, each one of the determined field numbers after storage and a generator to generate a predicted field number equal to that previously stored Field number plus the predicted number of the past Fields is that a tracking error detector is provided, which is compared under the control of that supplied by the detector Field numbers provide a tracking error indication when consecutive decoded digital numbers deviate from the predetermined sequence, and that the tracking error is a detected Specify tracking errors, and that also under the control of the tracking error display the pickup in another turn of the Spiral information track is provided in such a direction offsetting device that the detected tracking error is reduced will. 5) video disk player according to claim 4, characterized in that the comparison circuit for the comparison successively detected field numbers with the predicted field number determines whether the determined field number is within a predicted acceptable range of predicted Field numbers is or not. 6) Optical disc player for playing a sector divided Optical disk that has a spiral-shaped information track on its surface, which contains elements that are associated with represent a recorded carrier signal modulated to a video signal, the video signal comprising fields of information; each of which contains an information signal in a horizontal line, the sequentially arranged digital field numbers corresponding to the respective video field containing the information signal, the video signal being a contains a fixed number of video fields per spiral turn, with a pickup for sensing the recorded video signal, 1 3 0 0 1 7/081 2 1038397 and with a detector for the field numbers and with a Correlation circuit for correlating successive values of the field numbers determined with a previously determined one Field number, characterized by a memory for successive storage of successive ones detected fields, by a counter for counting a predetermined number of video fields, which after the Storing each one of the determined field numbers have passed, the counter being a generator for a predicted Contains field number equal to the previously stored field number plus the predicted number of past video fields is, and by a comparison circuit for comparing a successively detected field number with the predicted field number to determine whether the successively detected field number is within a predetermined acceptable range of the predicted field number or not. 7) Optical disc player for playing a sector divided Optical disk that has a spiral-shaped information track on its surface, which contains elements that are associated with represent a recorded carrier signal modulated to a video signal, the video signal containing fields of information; each of which contains an information signal in one horizontal line and wherein the information signal is one in succession represents arranged digital field number which corresponds to the respective video field containing the information signal and wherein the video signal contains a fixed number of video fields per spiral turn such that each of the fields: frame numbers represents sector information, with a pickup for sensing the recorded video signal and with a detector for the field numbers, as well as with a device for correlating successive values of the field numbers determined with a previously determined field number, identified by a memory for successive Storage of successive ascertained 130017/0812 3038387 Field numbers, by a counter for counting a predetermined one Number of video fields that have passed after one of the determined field numbers was stored, with the Counter contains a predicted field number generator, which is equal to the previously stored field number plus the predicted number of past video fields a first comparison circuit for comparing one sequentially detected field number with the predicted field number to determine whether the respective sector information of the determined field number and the predicted field number correspond to the same sector of the optical disc or not, and by a second comparison circuit to determine the difference between a successively determined field number and the predicted field number and for delivery an indication when that difference is within a predetermined acceptable range. 8) video disk player according to claim 7 for correlating successive Values of detected field numbers, the optical disk containing eight sectors per spiral turn and the Field numbers are represented in digital form, thereby characterized in that the first comparison circuit for comparing a successively determined field number with a predicted field number includes means for indicating when the least significant three Bits of the field number detected are equal to the least significant three bits of the predicted field number. 130017/0812